Heat exchangers currently being used have different forms and are furnished with different types of heat exchange elements that may be static or mobile such as tube coils having different dispositions (but not so far as the applicant is aware, spiral-shaped), hollow vanes or discs. Such known heat exchangers currently tend to suffer from deficiencies that may be detailed as: poor efficiency in heat exchange, lack of continuity in processing and poor agitation.
The present invention seeks to overcome the foregoing difficulties.
According to this invention there is provided a heat exchanger for crystallization of crystallizable suspensions whilst in motion. The heat exchanger includes a vertical cylindrical tank divided into an upper or deposit section containing an agitating vane and a processing section containing a plurality of superimposed subsections. Each superimposed subsection is partially defined by screens containing flow passes for the suspension, said screens being arranged such that alternate passes are in the periphery with the other passes in the centre. The heat exchanger also has heat exchanging elements located in each one of the subsections, an axial vertical shaft with internal ducts and labyrinths to which are coupled the agitating vane and the heat exchanging elements. There is also provided a frame located on the upper end of said shaft; which contains nozzles for feeding and venting the fluid that exchanges heat with said suspension, said frame resting on at least two hydraulic pistons, said pistons being located on a bridge at the upper part of the deposit section, and a discharge valve in the bottom of the lower subsection for processed suspension.
The location of the screens and of the suspension flow passes in each screen allow flow of the suspension downwardly and force it to travel horizontally inside each subsection. The direction of flow is alternately from the periphery toward the centre in some of the subsections and from the centre toward the periphery, in others. In the centre of the bottom of the lower subsections is located a suspension flow pass valve which upon opening permits establishment of flow of suspension through all subsections, one by one, downwardly.
The frame of the vertical shaft has feed and vent nozzles for the fluid that will exchange heat with the suspension, said nozzles forming part of the frame move along with it and are connected by means of flexible hoses to fixed nozzles. The vertical shaft has internal ducts and labyrinths for flow of heat exchange fluid directly toward the heat exchanger located in the lower subsection and also for, after circulating through continuous duct of said exchanger, going up to the next upper exchanger, and so forth, one by one, until the heat exchanger fluid outlets thrugh the vent nozzles located in the frame of the vertical shaft. The labyrinths of the vertical shaft are disposed such that, in the subsections wherein the suspension travels horizontally from the periphery toward the centre of the exchangers therein located, receive the heat exchanger fluid in their inner spiral and vent it into the outer spiral. In the alternated subsections in which suspension travels from the centre towards the periphery, the corresponding exchangers receive the heat exchanging fluid in the outer spiral and vent it into the inner spiral.
The present invention provides continuous heat exchange in that the suspension flows without interuption from the deposit section to the flow regulating valve located in the centre of the bottom of the lower subsection while the heat exchanging fluid feeds and vent continuously through the nozzles purposely located in the frame. Contra-directional heat exchange is produced by a preferred embodiment of this invention while the suspension descends from one subsection to another it travels in one horizontal direction, while the heat exchanging fluid travels in the opposite direction. Agitation is produced by the agitating vane as well as each one of the heat exchangers which are all subjected to a continuous movement of ascent and descent in each one of the sections or subsections while the suspension travels horizontally and continuously in each one of said subsections.